Substrate requirements for ion transport by rat intestine studied in vitro

Abstract

Ion transport by the jejunum and ileum of the rat was studied in vitro by a technique which presented a fluid of constant composition (Krebs-bicarbonate) to the mucosal surface of the gut over a period of 2 hours and permitted the direct collection of the transported fluid. Fluid transported by the jejunum was isosmotic with the mucosal fluid but had a lower concentration of Na, K and Cl and a higher concentration of HCO₃. The jejunum exhibited a very high rate of aerobic glycolysis and large amounts of lactate were present in its serosal fluid. Fluid transported by the ileum closely resembled the mucosal fluid in composition except for the partial replacement of bicarbonate by lactate. The rate of glycolysis was much lower in the ileum. When the glucose in the mucosal fluid was replaced by citrate or pyruvate, transport practically ceased in the jejunum but was little affected in the ileum. It was concluded that glycolysis provides an obligatory source of energy for ion transport by the jejunum.